1. Field of the Invention
The present invention relates to an automatic means for compensating for the voltage drop due to line resistance between an antenna receiver and a remotely located down converter and, more particularly, between a satellite dish antenna receiver and its down converter.
2. Discussion of the Prior Art
Recently, the use by consumers of antennas, particularly dish antennas, to receive satellite signals has substantially increased. Most consumers locate the satellite antenna in a convenient location remote from their house. Located at the satellite antenna is a low noise amplifier (LNA) and a down converter. Located at the house of the consumer is a receiver and, of course, the reception set. The receiver is conventionally interconnected with the down converter over two cables. The first cable, usually a pair of conductors, carries power to the down converter from the receiver and the second cable, usually a coaxial cable, carries the received signal from the down converter to the receiver and delivers the tuning voltage from the receiver to the down converter. A problem currently exists with the transmission of the tuning voltage, which is a DC voltage, over the cable to the down converter in that a portion of the voltage will be lost to the resistances of the cable. This cable resistance is a function of the cable length, the temperature of the environment, the overall deterioration of the cable, and the electrical characteristics of the various conventionally available LNAs and down converters. The voltage drop caused by the cable resistances can dramatically affect the tuning oscillator in the down converter and, therefore, it becomes imperative to control this voltage drop.
One conventional approach is to provide a compensation control potentiometer at the output of the tuning voltage from the receiver which can be adjusted by the installer at the site after installation of the LNA, the down converter and the cable. In other words, the installer adjusts the compensation potentiometer so that the signal received by the down converter is the proper tuning voltage. A second conventional approach is to provide a fine tuning circuit in the automatic frequency control (AFC) for the user. The user can set the desired channel and with the fine tune control compensate for any voltage and temperature variations due to cable resistance losses. While these two approaches are conventional and are both currently being used in satellite receivers, they are undesirable in that they do not provide total control over the voltage and temperature variations due to cable resistance losses or to the electrical characteristics of the remote equipment.
The present invention provides an automatic compensation control which eliminates the need for the added expense of the fine tune circuit and the compensation control potentiometer. Furthermore, it does not require any additional wiring or cable between the receiver and the down converter and, therefore, uses only the existing wires. Finally, the control of the present invention is automatic and continuously adjusts the circuit for any variations in cable resistance. In other words, the automatic compensation control of the present invention provides continuous monitoring of the cable resistance and automatically adjusts for cable voltage drops.